1. Field of the Invention
The present invention relates to a data storage device, and more particularly, to a data storage device using magnetic domain wall movement in a magnetic material and a method of operating the data storage device.
2. Description of the Related Art
A minute magnetic region that constitutes a ferromagnetic body is referred to as a magnetic domain. The rotation of all electrons in a magnetic domain, that is, the direction of their magnetic moments, is identical. The size and magnetization direction of a magnetic domain can be appropriately controlled by the property, shape and size of a magnetic substance and external energy.
A magnetic domain wall is a boundary portion between magnetic domains having different magnetization directions. The magnetic domain wall can be moved by an external magnetic field or by a current applied to a magnetic substance. That is, a plurality of magnetic domains having a specific magnetization direction can be formed in a magnetic layer having a predetermined width and thickness, and the magnetic domains and magnetic domain walls can be moved using a magnetic field or a current having an appropriate strength.
The principle of the magnetic domain wall movement can be applied to data storage devices. For example, when magnetic domains pass through a read/write head by movement of the magnetic domain wall, an operation of reading/writing data is possible without physical movement, e.g. rotating, of a recording medium. Accordingly, data storage devices, to which the principle of the magnetic domain wall movement is applied, do not require a word line for designating a cell, in which data is read (or written), unlike a usual random access memory (RAM), and it is not necessary to rotate a recording medium of such data storage devices unlike a hard disk drive (HDD). Since data storage devices using a magnetic domain wall movement have relatively simple structures and small bit sizes, a very large storage capacity of more than 1 tera bytes can be achieved.
However, since such data storage devices are in the first stage of development, several problems should be addressed so that these data storage devices may be put to practical use. In particular, there is a need to develop a method of recording data for practical use in a data storage device using the magnetic domain wall movement. Hereinafter, the problems of a writing operation in a conventional data storage device using a magnetic domain wall movement (hereinafter, referred to as a conventional writing operation) will be described.
The conventional writing operation can be classified into a method using an external magnetic field and a method using a spin torque phenomenon of electrons. The method using the spin torque phenomenon of electrons can be classified into a method using a giant magneto resistance (GMR) and a method using a tunnel magneto resistance (TMR).
The method using the external magnetic field can not be applied when a magnetic layer has great magnetic anisotropic energy, which means that a data storage device having good properties and high recording density can not be realized using the method using the external magnetic field.
In the method using the spin torque phenomenon of electrons, it is difficult to perform a writing operation when the thickness of a magnetic layer, in which data is to be recorded, is more than a predetermined thickness (i.e., about 3 nm). Accordingly, the method using the spin torque phenomenon of the electrons can not be applied to a perpendicular magnetic recording method requiring a magnetic layer having a thickness more than 100 nm. A TMR or GMR write head has a stack structure in which a ferromagnetic layer (a pinned layer), a separation layer (an insulating layer or a conductive layer) and a magnetic layer, in which data is to be recorded, are sequentially stacked. In a stacking process, since a surface of the separation layer may be damaged by etching, the properties of writing operations may deteriorate. In addition, since forming of the TMR or GMR write head requires multi-layer thin film processes, it is difficult to fabricate the TMR or GMR write head.
Accordingly, there is a need to develop a writing operation which is not limited by the properties and the dimensions of the magnetic layer, in which data is to be recorded, wherein the operation characteristics of writing operations are fundamentally prevented from deteriorating by a separation layer becoming damaged.
In addition, there is a need to develop a data storage device comprising a read head performing appropriate reading operations in connection with the above new writing method and a means for moving a magnetic domain wall.